The present invention relates to magnetoresistive heads, and more particularly to a method and system for providing a spin valve having a synthetic pinned layer which has reduced amplitude asymmetry and, in one embodiment, improved amplitude of the magnetoresistance.
Currently, spin valves are typically used for the magnetoresistive (MR) element in MR read heads. A spin valve includes a free layer and a pinned layer which are both magnetic. The free layer and pinned layer are separated by a nonmagnetic spacer layer. A spin valve also includes a conventional pinning layer, such as an antiferromagnetic (AFM) layer, that is used to pin the magnetization of the pinned layer in the desired direction. The pinned layer of a conventional spin valve is typically composed of a single magnetic material. The magnetic moment of the pinned layer is typically fixed by exchange coupling to the AFM layer. The spin valve may also include a capping layer. When used in a MR head, antiferromagnets or hard magnets are also typically used to ensure that the free layer has a single domain structure.
The magnetizations of the pinned layer and free layer are controlled in the conventional spin valve. The magnetizations of the pinned layer and free layer are typically biased to be orthogonal when no external field is applied. In other words, the pinning layer typically pins the magnetization of the pinned layer in a direction that is substantially ninety degrees from the direction of magnetization of the free layer when no recording media is being read. In a conventional MR head, the direction of magnetization of the pinned layer is approximately transverse, ninety degrees from the direction that current travels through the conventional spin valve.
The free layer is also typically biased to set the direction of magnetization of the free layer when no external field is applied. The free layer is typically biased using a combination of three fields. The combination of fields typically ensures that the free layer is biased longitudinally when no external field, for example from a recording media, is applied. Thus, the free layer is biased so that the magnetization is approximately in the direction that current flows through the conventional spin valve when no external field is applied. The fields which bias the free layer include a magnetic field generated by a bias current driven through the spin valve during use, an interlayer coupling between the pinned layer and the free layer, and the demagnetization field of the pinned layer. The combination of these three fields bias the free layer in the longitudinal direction
In order to improve the stability of the magnetization of the pinned layer, a synthetic pinned layer is used in synthetic spin valves. Such synthetic spin valves are substantially the same as conventional spin valves, except for the use of a synthetic pinned layer in lieu of a conventional pinned layer. Thus, the magnetization of the synthetic pinned layer is pinned in the transverse direction, ninety degrees from the longitudinal direction in which the magnetization of the free layer lies. Such synthetic pinned valves will be referred to as xe2x80x9csynthetic spin valves having a transverse pinned layerxe2x80x9d and the synthetic pinned layers will be referred to as xe2x80x9ctransverse synthetic pinned layers.xe2x80x9d The transverse synthetic pinned layer includes two magnetic layers that are separated by a nonmagnetic spacer layer. The two magnetic layers within the transverse synthetic pinned layer are antiferromagnetically coupled. Consequently, the net magnetic moment of the transverse synthetic pinned layer is significantly less than the magnetic moment for the conventional pinned layer.
Although the transverse synthetic pinned layer is more magnetically stable, the synthetic spin valve having a transverse pinned layer exhibits an undesirable asymmetry. The reduction in the magnetic moment of the transverse-synthetic pinned layer results in a demagnetization field from the transverse synthetic pinned layer that is less than the demagnetization field of the conventional pinned layer of the a conventional spin valve. Consequently, the combination of fields no longer biases the free layer in the longitudinal direction. The combination of the fields from the bias current and the interlayer coupling for the synthetic spin valve having a transverse pinned layer may be approximately the same as the demagnetization field of the conventional spin valve having the conventional pinned layer. However, because the demagnetization field of the transverse pinned layer is reduced, the three fields no longer bias the free layer of the synthetic spin valve having a transverse pinned layer longitudinally. Instead, the free layer may be less than ninety degrees from the transverse direction.
Because the magnetization of the free layer is tilted from the longitudinal direction in the absence of an external field, the response of the synthetic spin valve having a transverse pinned layer is asymmetric. Stored data in a recording media generate a magnetic field in a first direction or a magnetic field in a second direction. The second direction is opposite to the first direction. When the conventional spin valve reads the recording media, the free layer experiences fields due to the recording media. Because it is tilted from the longitudinal direction, the magnetization of the free layer will rotate more due to the field in one direction than the field in the other direction. The MR of the synthetic spin valve having a transverse pinned layer depends upon the difference in the directions of magnetization for the free layer and the transverse synthetic pinned layer. Because the free layer rotates more in one direction than the other, the MR of the synthetic spin valve having a transverse pinned layer is larger for fields from the recording media in one direction than the other. Consequently, the response of the synthetic spin valve having a transverse pinned layer is asymmetric. Asymmetry in the response is undesirable. If the asymmetry is large enough, the synthetic spin valve having a transverse pinned layer may be unusable.
Accordingly, what is needed is a system and method for reducing the asymmetry in a spin valve having a synthetic pinned layer. The present invention addresses such a need.
The present invention provides a method and system for providing a spin valve for use in a magnetoresistive head. The method and system comprise providing a synthetic pinned layer, a nonmagnetic spacer layer, and a free layer. The free layer has a first magnetization canted from a first direction by a first angle. The nonmagnetic spacer layer is disposed between the free layer and the synthetic pinned layer. The synthetic pinned layer has a second magnetization in a second direction. The second direction is canted from a third direction that is transverse to the first direction by a second angle. The second magnetization is substantially orthogonal to the first magnetization.
According to the system and method disclosed herein, the present invention provides a spin valve utilizing a synthetic free layer and which has reduced asymmetry. Furthermore, the amplitude of the magnetoresistive signal is improved.